diff --git a/crates/eip7702/src/auth_list.rs b/crates/eip7702/src/auth_list.rs
index 433769b..d1ee657 100644
--- a/crates/eip7702/src/auth_list.rs
+++ b/crates/eip7702/src/auth_list.rs
@@ -48,7 +48,7 @@ impl RecoveredAuthority {
 pub struct Authorization {
     /// The chain ID of the authorization.
     #[cfg_attr(feature = "serde", serde(with = "quantity"))]
-    pub chain_id: u64,
+    pub chain_id: U256,
     /// The address of the authorization.
     pub address: Address,
     /// The nonce for the authorization.
@@ -62,7 +62,7 @@ impl Authorization {
     /// # Note
     ///
     /// Implementers should check that this matches the current `chain_id` *or* is 0.
-    pub const fn chain_id(&self) -> u64 {
+    pub const fn chain_id(&self) -> U256 {
         self.chain_id
     }
 
@@ -496,7 +496,7 @@ mod tests {
     fn test_encode_decode_auth() {
         // fully filled
         test_encode_decode_roundtrip(Authorization {
-            chain_id: 1u64,
+            chain_id: U256::from(1),
             address: Address::left_padding_from(&[6]),
             nonce: 1,
         });
@@ -504,8 +504,11 @@ mod tests {
 
     #[test]
     fn test_encode_decode_signed_auth() {
-        let auth =
-            Authorization { chain_id: 1u64, address: Address::left_padding_from(&[6]), nonce: 1 };
+        let auth = Authorization {
+            chain_id: U256::from(1),
+            address: Address::left_padding_from(&[6]),
+            nonce: 1,
+        };
 
         let auth = auth.into_signed(PrimitiveSignature::from_str("48b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353efffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c8041b").unwrap());
         let mut buf = Vec::new();